The first time I rode Shimano’s Dura-Ace Di2, I had a funny reaction. As terrific as I thought it was, it struck me as not offering nearly the improvement it was destined to present when recruited for mountain bike use. The number of missed shifts I’ve suffered with a mechanical Dura-Ace drivetrain I could count on one, maybe two hands. But the number of missed shifts I’ve suffered—and I do mean suffered—on mountain bikes could roughly tally the number of mountain bike rides I’ve taken. The combination of bigger jumps between gears and the lower cadences common to mountain biking result in the sort of conditions that make flawless shifting unlikely.
Di whew
The thing about electronic shifting, for those who haven’t experienced it, is that it is unfailingly flawless. The closest the Deore XT Di2 has come to a missed shift was a slow downshift because I was starting from a dead stop in the 10t cog and my cadence was low. Once my cadence picked up a bit—we’re talking a half-dozen pedal strokes, it finished the shift. At low cadences in low gears, the downshifting can be a noticeable tick slower—we’re talking ¾ of a pedal revolution, but upshifts are stunningly quick, always.
I managed to run down the battery in my group a couple weeks ago, about ⅔ of the way through the ride, when I still had plenty of rolling terrain ahead. It turns out my record keeping on the number of hours of riding I did on that battery is not as complete as I thought, so I have to, instead, go with an estimate of more than 40 hours of riding, which scans relative to Shimano’s own estimates. They suggest a rider should get between 30 and 49 hours. Most of my riding isn’t on rolling terrain, so it’s not uncommon for me to only shift a few times on a longer climb and shift just a handful of times at the top of a descent before not shifting for the entire rest of the descent. Shimano quantifies battery life in another way: 600 to 1200 miles (1000-2000km) of riding.
One significant feature of the Di2 drivetrain is the removable battery. This means that so long as you haven’t been traveling with your MTB and have failed to relocate your spare battery to the new hydration pack (cough, cough), you needn’t worry about ever draining the battery during a ride. Simply pop the battery cover off and slide the fresh one in.
Every bit as consequential a decision as the removable battery was the move to wireless operation. No wires and no finicky eTube programming has made life much more enjoyable and reliable.
One criticism leveled at Shimano’s road Di2 groups has been insufficient tactile feedback for shifts. Button travel was so short and the haptic feedback, that is, the sense of a click, was so minimal and to be lost when wearing long-finger gloves. With Deore XT Di2 the button travel is long enough to make each shift a definitive action, with one exception.
I noticed that one some rowdier descents the knuckle of my thumb bumped the downshift button. Well, that’s not quite right. I didn’t notice the knuckle bumping the button. What I noticed was that on multiple occasions when I sat down to resume pedaling, the chain would downshift a cog or two. It happened three or four times before I realized I needed to position my hand a half centimeter to the right.
If you press and hold one of the shift buttons, the multishift feature will either dump the chain in the 10 or downshift to the 51. Honestly, I’ve yet to encounter a situation where I needed to shift more than three cogs, but I’ve experienced terrain where a rapid five-cog change would be handy.
Shimano offers programmability with the Di2 shifter, but I’ve always resisted coming up with my own setup for lever function—particularly with their road levers—because I’ve never wanted the confusion of getting on another bike where the levers operate differently than my muscle memory expects. Should I continue to experience knuckle-bump shifts, I might consider reversing the function of the two buttons, but I’m more likley to move the shifter inboard a bit. Features like autoshift and button reprogramming lose some of their luster with 1x drivetrains. On eMTBs using Shimano’s EP motors, autoshift becomes an option, and I have to admit that’s an intriguing idea.
The other option for solving the button bump is to adjust their positions a bit more; both sit on ball joints, making their positioning remarkably variable.
Range
Shimano offers XT chainrings from 28 to 36 teeth, in 2-tooth increments. I went with the 28t ring for a few reasons. Two two biggest reasons were that I often do rides that result in 200 feet of climbing per mile and I’m not the fast guy I once was. So there’s that. There’s also the fact that I think in general most drivetrains are over-geared for most of us. I’ve used the 10t cog on the 10-51 cassette on road descents, which makes me question its usefulness.
The new cassette features teeth that are thicker at the base to improve durability, according to Shimano. And in addition to the 10-51 cassette, which uses a long-cage derailleur, Shimano also offers a shorter cage (I can’t call it “short” in an absolute sense) derailleur which pairs with a 9-45 cassette, which sounds pretty terrific for areas of the country that lack steep climbs, though I wonder how often those parts will be spec’d on bikes (hint: not at all, unfortunately, due to inventory needs).
Stop, not go
While the drivetrain may be the big story with this group, it’s not the only story. I can’t stress enough just how good the brakes are. Four-piston disc brakes changed the way I brake, just as disc brakes on road bikes changed the way I brake. Rather than gradually braking, and using modulation to adjust my speed, I brake later and harder, often less because I’ve come to appreciate the ability of the brakes to handle it than my own need based on changes in terrain.
The big change in the brakes from M8100 to M8200 is thermal consistency. Riders will talk about a wandering bite point, which is how far you pull the lever before the pads engage. Honestly, I’ve only experienced variability with the Deore XT brakes on one descent, and it took an extended descent with no stopping to get there. For me, wandering bite point was really only an issue with XTR. Shimano says a new mineral oil, resin pistons and redesigned seals all contributed to superior thermal consistency with the new brakes.
I’m running them with 180mm rotors, and while larger rotors—now thicker—are available, my speed rarely tops 30 mph, which is more a function of straightaway length than nerve. As a result, larger rotors would be overkill, and smaller ones would undermine some of my confidence.
I’ve written previously about my preference for Deore XT over XTR. That wasn’t always the case, but it has been for a solid 20 years at this point. The greater braking power, the lack of flex in the levers, the inherently less finicky braking and shifting overall and the increased durability make the greater weight of the Deore XT Di2 group simply a cost, not a bug. It would be silly to call the greater weight a feature, but it is clearly a necessity, and one that I accept without reservation.
Shimano still offers a traditional 2-piston brake and in the same way there is terrain that makes the 9-45 cassette a smart choice, riding on flatter terrain doesn’t necessitate a 4-piston brake
And another thing
Shimano offers a neverending list of improvements over the previous group, cartridge bearings replacing cup-and-cone, but in day-to-day riding the other notable improvement I experience is the faster freehub engagement. It’s down to 3.5 degrees from 6.7 degrees, a not-quite 50% reduction. That’s handy in rock gardens where I need to stutter-stroke my way through the bumpy stuff.
Cost
The Deore XT Di2 group goes for $2099 at suggested retail. The wheelset, whether 27.5 or 29 goes for another $570. Shimano offers both brake and drivetrain kits should you want to upgrade part, but not all, of your bike.
There’s another kind of cost—the attention you must devote to the operation of your bike. Every missed shift, every howling brake, every overshot braking point is a distraction that takes you out of your ride, interrupting your opportunity to enter flow. The highest praise we can offer components is to say they don’t call attention to themselves. That’s precisely the point of Deore XT Di2: You focus on the ride, not your bike.
Final thought: When I tell you Deore XT Di2 is forgettable, I’m praising it.